Many high power laser diodes consist of a linear array of emitters. As the emitters have to be separated for thermal and optical reasons, it is not uncommon to have the emitter array extend beyond 10 mm. When mounting such an array onto a heat sink it is difficult to keep it flat, thus the emitters are no longer in a straight line. This deviation from straightness is known in the art as "smile". For a 10 mm wide diode the "smile" is typically from 1 to 10 microns. Due to the high divergence angle of laser diodes the focal length of the coupling lenses used (known as "microlenses") is very short. When a cylindrical lens is used as a fast axis microlens, as shown in FIG. 1, the slightest deviation from straightness prevents the image of the emitters from forming a straight line (or overlapping lines). For example, in FIG. 1 when using a cylindrical lens 4, having a focal length of about 1 mm, a 10 micron "smile" will cause the images of the emitters to bow by 1 mm when projected 100 mm from diode. Prior art methods such as U.S. Pat. No. 5,619,245 attempt to correct the "smile" by optical means, requiring extra optical elements and increasing the numerical aperture of the optics. The present invention corrects the "smile" in a simple manner. Other prior art, such as U.S. Pat. No. 5,420,722 bend the cylindrical lens to match the straightness error of the laser diode. Bending the microlens can provide corrections for simple deviations from straightness but not for complex curves.